I think David adressing Mr Ellis as "T-Rex Sensei" is not disrespectful at all and he (Mr Ellis) would like the apellative. I believe he would like to be called himself a dinosaur in the aikido world of today, as he calls dinosaurs his masters
from back in the day.
Perhaps the tag of T Rex Sensei is a private joke between Henry and David?I know Henry has a good sense of humour. As it happens I might myself qualify as a member of the dinosaur age!! Cheers, Joe.